Control Of Local Blood Flow Research Articles

Detection of Human Red Blood Cell-bound Nitric Oxide

Major disparities in reported levels of basal human nitric oxide metabolites have resulted in a recent literature focusing almost exclusively on methods. We chose to analyze triiodide chemiluminescence, drawn by the prospect of identifying why the most commonly employed assay in nitric oxide biology typically yielded lower metabolite values, compared with several other techniques. We found that the sensitivity of triiodide was greatly affected by the auto-capture of nitric oxide by deoxygenated cell-free heme in the reaction chamber. Potential contaminants and signal losses were also associated with standard sample purification procedures and the chemistry involved in nitrite removal. To inhibit heme nitric oxide auto-capture, we added potassium ferricyanide to the triiodide reagent, reasoning this would provide a more complete detection of any liberated nitric oxide. From human venous blood samples, we established nitric oxide levels ranging from 0.000178 to 0.00024 mol nitric oxide/mol hemoglobin. We went on to find significantly elevated nitric oxide levels in venous blood taken from diabetic patients in comparison to healthy controls (p < 0.0001). We concluded that the lack of signals reported of late by several groups using triiodide chemiluminescence for the detection of hemoglobin-bound nitric oxide may not represent levels on the border of assay sensitivity but rather underestimated values because of methodological limitations. We therefore stress the need for assay systems to be developed that differentiate between individual nitric oxide metabolite species and overcome the limitations we outline, allowing accurate conclusions to be drawn regarding physiological nitric oxide metabolite levels.

Reduced Arteriolar Responses to Skeletal Muscle Contraction after Ingestion of a High Salt Diet

We previously reported that in skeletal muscle arterioles of rats fed a very high salt (HS; 7%) diet, the bioavailability of endothelium-derived nitric oxide (NO) is reduced through scavenging by reactive oxygen species. Because arteriolar NO can play an important role in local blood flow control, we investigated whether arteriolar responses to increased tissue metabolism become compromised in skeletal muscle of salt-fed rats. Consumption of a HS (4%) diet for 4 weeks had no effect on arteriolar diameters, volume flow or shear stress in resting spinotrapezius muscle. Arteriolar responses to a modest elevation in metabolic demand (0.5 Hz contraction) were not different from those in rats fed a normal diet, but diameter responses to a greater elevation in metabolic demand (4 Hz contraction) were significantly less in HS rats than in rats fed a normal diet. In both groups, the NO synthase inhibitor N^G-monomethyl-L-arginine reduced resting arteriolar diameters and flow by a similar amount and had little or no effect on arteriolar diameter or flow responses to muscle contraction. Arterioles in HS rats exhibited an increase in overall oxidant activity (tetranitroblue tetrazolium reduction) but not in superoxide activity (dihydroethidine oxidation). Reactive oxygen species scavengers (2,2,6,6-tetramethylpiperidine-N-oxyl and catalase) did not normalize the reduced arteriolar responses to muscle contraction in HS rats. These findings suggest that increased oxidant activity in the arteriolar network of salt-fed rats is not due to accumulation of superoxide anion and that neither this oxidant activity nor reduced NO availability can account for the blunted active arteriolar dilation in rats fed a 4% salt diet.

A Comparison of Changes in Rhythms of Sacral Skin Blood Flow in Response to Heating and Indentation

Brienza DM, Geyer MJ, Jan Y-K. A comparison of changes in rhythms of sacral skin blood flow in response to heating and indentation. Arch Phys Med Rehabil 2005;86:1245–51. Objective To differentiate blood flow control mechanisms associated with indentation from those associated with heating and to discern heat-induced and pressure-induced changes by comparing the effect of externally applied stress on skin blood flow (SBF) to the response to externally applied heat. Design Repeated-measures design. Setting A university research laboratory. Participants Ten healthy, young adults (5 men, 5 women; mean age ± standard deviation, 30.0±3.1y). Intervention Incremental heat (35°−45°C, 1° step/min) and pressure (0–60mmHg, 5mmHg step/3min) on the sacrum using a computer-controlled indenter. Sessions for heat and pressure protocols were separated by 7±2 days. Main Outcome Measures We used a Laserflo Blood Perfusion Monitor 2 and Softip pencil probe to measure capillary blood perfusion and wavelet analysis to decompose the blood flow signal. The power spectrum was divided into 5 ranges corresponding to metabolic, neurogenic, myogenic, respiratory, and cardiac control mechanisms. The average relative (ie, normalized) power in each frequency range was computed to determine of the relative contribution of each control mechanism. Results Power in the myogenic frequency range was higher after incremental pressure and lower after incremental heating, whereas power in the metabolic frequency range was lower after incremental pressure and higher after incremental heating ( P<.01). Mean blood flow decreased as pressure increased from 0 to 15mmHg; mean blood flow increased as pressure increased from 15 to 60mmHg. Conclusions SBF, as recorded by the laser Doppler, suggests that there may be a myogenic control mechanism mediating blood flow after incremental tissue loads and that a metabolic control mechanism may mediate blood flow after heat application to the tissue. The study of local blood flow control mechanisms and their response to pathomechanical perturbations may be possible using wavelet analysis of blood flow oscillations. More research is needed to establish the clinical utility of these findings in the development of support surfaces intended to reduce the risk of developing pressure ulcers.

Plasma ATP during exercise: possible role in regulation of coronary blood flow

It was previously shown that red blood cells release ATP when blood oxygen tension decreases. ATP acts on microvascular endothelial cells to produce a retrograde conducted vasodilation (presumably via gap junctions) to the upstream arteriole. These observations form the basis for an ATP hypothesis of local metabolic control of coronary blood flow due to vasodilation in microvascular units where myocardial oxygen extraction is high. Dogs (n = 10) were instrumented with catheters in the aorta and coronary sinus, and a flow transducer was placed around the circumflex coronary artery. Arterial and coronary venous plasma ATP concentrations were measured at rest and during three levels of treadmill exercise by using a luciferin-luciferase assay. During exercise, myocardial oxygen consumption increased approximately 3.2-fold, coronary blood flow increased approximately 2.7-fold, and coronary venous oxygen tension decreased from 19 to 12.9 mmHg. Coronary venous plasma ATP concentration increased significantly from 31.1 to 51.2 nM (P < 0.01) during exercise. Coronary blood flow increased linearly with coronary venous ATP concentration (P < 0.01). Coronary venous-arterial plasma ATP concentration difference increased significantly during exercise (P < 0.05). The data support the hypothesis that ATP is one of the factors controlling coronary blood flow during exercise.

Critical role for transient receptor potential channel TRPM4 in myogenic constriction of cerebral arteries.

Local control of cerebral blood flow is regulated in part through myogenic constriction of resistance arteries. Although this response requires Ca2+ influx via voltage-dependent Ca2+ channels secondary to smooth muscle cell depolarization, the mechanisms responsible for alteration of vascular smooth muscle (VSM) cell membrane potential are not fully understood. A previous study from our laboratory demonstrated a critical role for a member of the transient receptor potential (TRP) superfamily of ion channels, TRPC6, in this response. Several other of the approximately 22 identified TRP proteins are also present in cerebral arteries, but their functions have not been elucidated. Two of these channels, TRPM4 and TRPM5, exhibit biophysical properties that are consistent with a role for control of membrane potential of excitable cells. We hypothesized that TRPM4/TRPM5-dependent currents contribute to myogenic vasoconstriction of cerebral arteries. Cation channels with unitary conductance, ion selectivity and Ca2+-dependence similar to those of cloned TRPM4 and TRPM5 were present in freshly isolated VSM cells. We found that TRPM4 mRNA was detected in both whole cerebral arteries and in isolated VSM cells whereas TRPM5 message was absent from cerebral artery myocytes. We also found that pressure-induced smooth muscle cell depolarization was attenuated in isolated cerebral arteries treated with TRPM4 antisense oligodeoxynucleotides to downregulate channel subunit expression. In agreement with these data, myogenic vasoconstriction of intact cerebral arteries administered TRPM4 antisense was attenuated compared with controls, whereas KCl-induced constriction did not differ between groups. We concluded that activation of TRPM4-dependent currents contributed to myogenic vasoconstriction of cerebral arteries.

Applied cerebrovascular physiology

The understanding and manipulation of cerebrovascular physiology is essential in the management of head injuries and anaesthesia for neurosurgery. The high metabolic requirements (20% of basal oxygen and 25% of basal glucose consumption) and blood flow (15% of the cardiac output) emphasize the need to ensure adequate substrate delivery for the production of energy to transmit electrical impulses and maintain ionic gradients across cell membranes. The cerebral microenvironment is responsible for a blood-brain barrier with unique properties affecting ionic and fluid distribution, active transport mechanisms and drug distributions. The rigid cranium with its contents of parenchyma, CSF, blood and interstitial fluid creates pressure and volume relationships with implications in pathological processes as well as targets for therapy. Physiological determinants of cerebral blood flow and volume include flow-metabolism coupling, autoregulation, carbon dioxide and oxygen arterial tensions, temperature, haematocrit, venous pressures, and the autonomic nervous system. Local metabolic control of regional cerebral blood flow is mediated by actions on vascular tone (vasodilators and vasoconstrictors). The roles of nitric oxide, prostaglandins, adenosine, cations (potassium and calcium) and endothelin are noteworthy. Estimations of cerebral blood flow and oxygenation are essential to assess and to manipulate cerebrovascular physiology. Global and local techniques are briefly discussed including the Kety-Schmidt technique, xenon-133 washout, imaging (dynamic CT, SPECT, PET, and fMRI) jugular venous oximetry, transcranial Doppler, brain tissue oxygenation and intracerebral microdialysis.

Commentary

HIGHLIGHTED TOPICSSkeletal and Cardiac Muscle Blood FlowCommentaryGary C. SieckGary C. SieckPublished Online:01 Jul 2004https://doi.org/10.1152/japplphysiol.00415.2004MoreSectionsPDF (11 KB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInEmailWeChat This issue of the Journal is the first in our third Highlighted Topics series for 2004, “Skeletal and Cardiac Muscle Blood Flow.” Two of the articles featured in this issue deserve special comment for their important contributions to this highlighted area of research. In the first featured article, entitled “Role of nitric oxide in exercise sympatholysis,” Dr. J. Buckwalter and colleagues (1) examine whether production of nitric oxide is responsible for the attenuated responsiveness of α1- and α2-adrenergic receptors in exercising skeletal muscle. Vascular tone in exercising muscle appears to be a balance between vasoconstriction, necessary for blood pressure regulation, and vasodilation, necessary for oxygen delivery. Although there is clearly sympathetic vasoconstriction in exercising muscle, the ability of the sympathetic nervous system to induce vasoconstriction in active skeletal muscle appears to be less than that at rest. The mechanism responsible for this attenuation has yet to be definitively established. In this study examining exercising canine skeletal muscle, these investigators found that nitric oxide plays a role in reducing α1-adrenergic receptor responsiveness. However, α2-adrenergic receptor responsiveness was unaffected by nitric oxide synthase inhibition. The results of this study provide insight into local control of skeletal muscle blood flow during exercise and suggest that nitric oxide production is not the sole mechanism for attenuation of sympathetic vasoconstriction in contracting skeletal muscle.Approximately 30% of patients treated with stents develop restenosis at the site of stent implantation as a result of neointimal hyperplasia. Studies in recent years have extensively explored a putative relationship linking altered vascular geometry and indexes of wall shear stress to neointimal hyperplasia, reductions in cardiac blood flow, and regional myocardial ischemia. In the second featured article, entitled “Stent design properties and deployment ratio influence indexes of wall shear stress: a three-dimensional computational fluid dynamics investigation within a normal artery,” Dr. J. LaDisa, Jr., and colleagues (2) used three-dimensional computational fluid dynamics modeling to test their hypothesis that the geometric parameters of an implanted stent influence acute distributions of wall shear stress. These investigators found that reducing the thickness of stent struts caused an appreciable reduction in the area of the vessel exposed to elevated spatial gradients of wall shear stress and also reduced the distributions of wall shear stress implicated in the development of neointimal hyperplasia. Increasing both the number of struts and the stent-to-artery deployment ratio also increased vascular exposure to low wall shear stress. These results, together with recent in vivo studies, suggest that local vascular geometry after stent implantation influences the distribution of wall shear stress, which, in turn, may mediate neointimal hyperplasia in response to vascular injury. The application of such findings to novel stent designs that limit adverse alterations in indexes of wall shear stress after implantation may reduce the risk of restenosis and may help maintain perfusion distal to vascular stenoses.REFERENCES1 Buckwalter JB, Taylor JC, Hamann JJ, and Clifford PS. Role of nitric oxide in exercise sympatholysis. J Appl Physiol 97: 417–423, 2004.Link | ISI | Google Scholar2 LaDisa JF, Olson LE, Guler I, Hettrick DA, Audi SH, Kersten JR, Warltier DC, and Pagel PS. Stent design properties and deployment ratio influence indexes of wall shear stress: a three-dimensional computational fluid dynamics investigation within a normal artery. J Appl Physiol 97: 424–430, 2004.Link | ISI | Google Scholar Download PDF Previous Back to Top Next FiguresReferencesRelatedInformation More from this issue > Volume 97Issue 1July 2004Pages 416-416 Copyright & PermissionsCopyright © 2004 the American Physiological Societyhttps://doi.org/10.1152/japplphysiol.00415.2004History Published online 1 July 2004 Published in print 1 July 2004 Metrics

Gender-specific regulation of cardiovascular function: estrogen as key player.

This review provides an overview of gender-specific differences in the incidence and development of cardiovascular diseases, including hypertension, atherosclerosis, heart failure and the corresponding myocardial remodeling. The review discusses the possible mechanisms by which estrogen affords a beneficial effect on cardiovascular function via genomic vs non genomic regulation; estrogen receptor-dependent vs estrogen receptor-independent pathways, specific signal transduction cascades, especially those involving protein kinase B (Akt) and mitogen activated protein kinase (MAPK), as well as their downstream targets, such as nitric oxide synthase, cyclooxygenase, cytochrome P450 (CYP), NADPH oxidase and superoxide dismutase. Having considered the essential role of the microcirculation in the control of vascular resistance in vivo, estrogen-related regulation of microvascular function and blood pressure is highlighted. Attention is focused on the effects of estrogen on pressure (myogenic)-dependent and flow/shear stress-dependent mechanisms of arterioles, which contribute significantly to the control of local blood flow and peripheral resistance via alterations in the release of endothelial mediators, such as nitric oxide, prostaglandins and endothelium-derived hyperpolarizing factor.

Communication between endothelial and smooth muscle cells

Vascular endothelial cells play a fundamental role in the control of vascular tone, and therefore in the control of local blood flow, by releasing various contracting (endothelin, prostaglandins) and relaxing (prostacycline, NO) factors. An additional mechanism involving the hyperpolarization of the vascular smooth muscle cells is observed mainly in the coronary vascular bed and in the periphery. This phenomenon was attributed to an elusive endothelial factor called endothelium-derived hyperpolarizing factor (EDHF). This mechanism is now better understood. It involves first an increase in the endothelial intracellular concentration of calcium, the activation of endothelial potassium channels and the resulting hyperpolarization of the endothelial cells. The hyperpolarization of the endothelial cells is transmitted to the smooth muscle cells by different pathways. This hyperpolarization propagates along the vessels not only via the smooth muscle cells but also via the endothelial cells. Therefore, the endothelial layer can also be considered as a conducting tissue. The discovery of specific inhibitors of the endothelial cell hyperpolarization allows the assessment of the contribution of EDHF-mediated responses in the control of vascular tone.

LOCAL THERMAL CONTROL OF SKIN BLOOD FLOW IN DIABETES

Local temperature has an important role in the control of the skin circulation in humans, and can change skin blood flow from zero to maximal levels. Vasodilation to local warming of the skin includes important roles for sensory nerves and nitric oxide. In individuals with type 2 diabetes mellitus (DM), cutaneous vascular function is impaired, but the mechanisms are not well understood. PURPOSES To test whether local warming vasodilation is altered in type 2 DM, and to test whether hyperglycemia per se has a role in altered local control of skin blood flow in diabetes. METHODS 1. We used nonpainful local warming (42°C) of the skin in combination with laser-Doppler measurement of skin blood flow in individuals with type 2 DM and in age-matched controls. 2. In separate studies, we measured responses to similar local warming in healthy individuals during acute hyperglycemia induced by intravenous infusion of glucose with simultaneous insulin, somatostatin, glucagon and growth hormone infusions to keep all other hormones at baseline physiological levels. RESULTS Preliminary results indicate diminished vasodilation to nonpainful local warming in patients with type 2 DM compared to controls, including a decrease of ∼20% in both the initial peak (sensory nerve mediated) and final plateau (NO dependent) phases of the response. Acute hyperglycemia in healthy subjects did not alter cutaneous vasodilation to local warming. CONCLUSION Cutaneous vasodilation to nonpainful local warming is impaired in type 2 DM. Although one episode of acute hyperglycemia did not affect this response in healthy subjects, this impairment in patients may be a result of repeated episodes or higher levels of hyperglycemia in the development of the disease. Supported by NIH DK-29953, HL-63328, AR-08610 and GCRC grant RR-00585 (to the Mayo Clinic).

Significant Variation of the Elevated Nitric Oxide Levels in Aqueous Humor from Patients with Different Types of Glaucoma

Though several studies have shown that the biochemical function of nitric oxide (NO) in the eye might play an important role in the regulation of intraocular pressure (IOP), local control of ocular blood flow and loss of retinal ganglion cells by apoptosis, it is unclear whether the role of NO is similar in the pathogenesis of different kinds of glaucoma: primary open-angle glaucoma (POAG), chronic closed-angle glaucoma (CCAG) and neovascular glaucoma (NVG). To further explore this issue, we measured the concentrations of NO in aqueous humor and plasma samples from patients with POAG (n = 31), CCAG (n = 76), NVG (n = 8) and cataract (n = 30). All of the NVG patients suffered from severe proliferative diabetic retinopathy, while other patients were free of any other systemic disease. The NO levels in both aqueous humor and plasma samples were assessed by chemiluminescence assay. We found that the NO levels in aqueous humor samples were greatly varied in patients with POAG (36.2 ± 3.3 µM), CCAG (47.7 ± 3.4 µM) and NVG (65.8 ± 5.4 µM), and all of them were significantly higher than in cataract patients (27.0 ± 2.9 µM; p < 0.05). Except NVG patients whose NO levels in plasma samples were highest (24.1 ± 3.5 µM) among all groups, the plasma NO levels were not significantly different between the other glaucoma patients and the cataract patients. We therefore concluded that significant variation of the elevated NO levels in aqueous humor samples from the patients with different types of glaucoma may reflect their differences in the pathogenesis.

Perivascular nerves and vascular endothelium: recent advances.

Within the last few years, advances have been made regarding perivascular nerves and the endothelium of the vascular system, both potentially important in the understanding of the mechanisms of local control of blood flow. Endothelin-1 (ET-1) has been identified in rat cerebrovascular nerves, neuropeptide Y (NPY) has been demonstrated in umbilical endothelium, the arginine-vasopressin (VP) system has been discovered in the heart (including coronary endothelium), and P2X receptors have been observed in vascular endothelial cells. After a brief introduction to vascular biology, this review will focus on the above-mentioned new data.

Lack of flow regulation may explain the development of arteriovenous malformations

In the normal vasculature, vessels of widely different sizes maintain shear stress within a narrow range. Recently, investigators have had great success using mathematical models to explore the relationship of structure to function in normal vascular beds. When investigators first explored how vascular beds adapt to set shear stress at appropriate levels, however, some vessels tended to regress, and some tended to grow into arteriovenous shunts. Degeneration of the arterial tree is prevented when flow regulation is added to the model. The present work explores the implication of this theoretical development and illustrates how it may explain the genesis of arteriovenous malformations (AVMs). We use a simple model to illustrate how impairing local control of blood flow causes models to become structurally unstable, yielding a structure and behavior similar to AVMs. This work shows how the lack of local flow control can be the cause, not just the result, of arteriovenous malformations. With insight gained from this modeling approach, specific, focused experiments can be designed. [Neurol Res 2001; 23: 641-644]

The influence of topical capsaicin on the local thermal control of skin blood flow in humans.

To test whether heat-sensitive receptors participate in the cutaneous vascular responses to direct heating, we monitored skin blood flow (SkBF; laser Doppler flowmetry) where the sensation of heat was induced either by local warming (T(Loc); Peltier cooling/heating unit) or by both direct warming and chemical stimulation of heat-sensitive nociceptors (capsaicin). In part I, topical capsaicin (0.075 or 0.025%) was applied to 12 cm(2) of skin 1 h before stepwise local warming of untreated and capsaicin-treated forearm skin. Pretreatment with 0.075% capsaicin cream shifted the SkBF/T(Loc) relationship to lower temperatures by an average of 6 +/- 0.8 degrees C (P < 0.05). In part II, we used a combination of topical capsaicin (0.025%) and local warming to evoke thermal sensation at one site and only local warming to evoke thermal sensation at a separate site. Cutaneous vasomotor responses were compared when the temperatures at these two sites were perceived to be the same. SkBF differed significantly between capsaicin and control sites when compared on the basis of actual temperatures, but that difference became insignificant when compared on the basis of the perceived temperatures. These data suggest heat-sensitive nociceptors are important in the cutaneous vasodilator response to local skin warming.

Identification of receptors for neuromedin U and its role in feeding.

Neuromedin U (NMU) is a neuropeptide with potent activity on smooth muscle which was isolated first from porcine spinal cord and later from other species. It is widely distributed in the gut and central nervous system. Peripheral activities of NMU include stimulation of smooth muscle, increase of blood pressure, alteration of ion transport in the gut, control of local blood flow and regulation of adrenocortical function. An NMU receptor has not been molecularly identified. Here we show that the previously described orphan G-protein-coupled receptor FM-3 (ref. 15) and a newly discovered one (FM-4) are cognate receptors for NMU. FM-3, designated NMU1R, is abundantly expressed in peripheral tissues whereas FM-4, designated NMU2R, is expressed in specific regions of the brain. NMU is expressed in the ventromedial hypothalamus in the rat brain, and its level is significantly reduced following fasting. Intracerebroventricular administration of NMU markedly suppresses food intake in rats. These findings provide a molecular basis for the biochemical activities of NMU and may indicate that NMU is involved in the central control of feeding.

Types of neurons in the enteric nervous system

This paper, written for the symposium in honour of more than 40 years’ contribution to autonomic research by Professor Geoffrey Burnstock, highlights the progress made in understanding the organisation of the enteric nervous system over this time. Forty years ago, the prevailing view was that the neurons within the gut wall were post-ganglionic neurons of parasympathetic pathways. This view was replaced as evidence accrued that the neurons are part of the enteric nervous system and are involved in reflex and integrative activities that can occur even in the absence of neuronal influence from extrinsic sources. Work in Burnstock’s laboratory led to the discovery of intrinsic inhibitory neurons with then novel pharmacology of transmission, and precipitated investigation of neuron types in the enteric nervous system. All the types of neurons in the enteric nervous system of the small intestine of the guinea-pig have now been identified in terms of their morphologies, projections, primary neurotransmitters and physiological identification. In this region there are 14 functionally defined neuron types, each with a characteristic combination of morphological, neurochemical and biophysical properties. The nerve circuits underlying effects on motility, blood flow and secretion that are mediated through the enteric nervous system are constructed from these neurons. The circuits for simple motility reflexes are now known, and progress has been made in analysing those involved in local control of blood flow and transmucosal fluid movement in the small intestine.

Nonadrenergic innervation of the rat laryngeal vasculature

In order to gain a better understanding of the central and local control of laryngeal blood flow, the vascular innervation to the rat laryngeal muscles was examined. To visualize the vascular network, the animals were perfused with a gelatin/India ink solution. The larynges were removed and fixed. The superior laryngeal, cricothyroid, and inferior laryngeal arteries (all branch off the superior thyroid artery) were dissected in continuity into their respective muscles. Specimens were reacted in toto using immunohistochemical techniques for the presence of neuropeptide-Y (NPY), vasoactive intestinal peptide (VIP), calcitonin gene related peptide (CGRP), and neuronal nitric oxide synthase (NOS-1). Results show that all of the laryngeal vasculature is richly innervated by fibers containing these peptides. Qualitatively, the most prominent of these is NPY in association with the superior and the inferior laryngeal arteries, followed by VIP and NOS-1, and finally CGRP distributed equally on all the vessels. Immunopositive fibers are found along the entire course of the feeding arteries, beginning with the superior thyroid artery and continuing down to small arterioles into the terminal vascular beds. These peptides can act as vasodilators, vasoconstrictors, and/or neuromodulators and may work synergistically or antagonistically with other transmitters in controlling laryngeal blood flow. Their effects are dependent on the specific vascular bed in question, that is, in some areas they are vasodilators, in others vasoconstrictors, and in other neuromodulators. What effects they have on the laryngeal vasculature and how they interact within the larynx have yet to be determined. Anat Rec 259:180–188, 2000. © 2000 Wiley-Liss, Inc.

Nonadrenergic innervation of the rat laryngeal vasculature.

In order to gain a better understanding of the central and local control of laryngeal blood flow, the vascular innervation to the rat laryngeal muscles was examined. To visualize the vascular network, the animals were perfused with a gelatin/India ink solution. The larynges were removed and fixed. The superior laryngeal, cricothyroid, and inferior laryngeal arteries (all branch off the superior thyroid artery) were dissected in continuity into their respective muscles. Specimens were reacted in toto using immunohistochemical techniques for the presence of neuropeptide-Y (NPY), vasoactive intestinal peptide (VIP), calcitonin gene related peptide (CGRP), and neuronal nitric oxide synthase (NOS-1). Results show that all of the laryngeal vasculature is richly innervated by fibers containing these peptides. Qualitatively, the most prominent of these is NPY in association with the superior and the inferior laryngeal arteries, followed by VIP and NOS-1, and finally CGRP distributed equally on all the vessels. Immunopositive fibers are found along the entire course of the feeding arteries, beginning with the superior thyroid artery and continuing down to small arterioles into the terminal vascular beds. These peptides can act as vasodilators, vasoconstrictors, and/or neuromodulators and may work synergistically or antagonistically with other transmitters in controlling laryngeal blood flow. Their effects are dependent on the specific vascular bed in question, that is, in some areas they are vasodilators, in others vasoconstrictors, and in other neuromodulators. What effects they have on the laryngeal vasculature and how they interact within the larynx have yet to be determined.

Comparison of the vascular innervation of the rat cochlea and vestibular system

In order to gain a better understanding of the neuronal and local control of inner ear blood flow, the vascular innervation to the rat cochlea and vestibular system was examined. Specimens were removed in toto beginning at the basilar artery extending to the anterior inferior cerebellar artery, labyrinthine artery, common cochlear artery, modiolar artery and anterior vestibular artery. When possible the vessels were dissected in continuity through the cribrose area. The vestibular endorgans were also removed. Specimens were examined using immunohistochemical techniques for the presence of vasoactive intestinal peptide, neuronal nitric oxide synthase, neuropeptide-Y, substance P and calcitonin gene related peptide. Results show that the vasculature to the cochlea and vestibular portion of the inner ear receive similar types of nonadrenergic innervation, that within the vestibular endorgans, only CGRP and SP were found in the neuroepithelium or in association with vessels, and that within the vestibular system, the majority of the vascular innervation appears to stop at or near the cribrose area. In the cochlea however, it extends to include the radiating arterioles. These findings suggest that cochlear blood flow is under finer control and that neuronally induced changes in blood flow may have a more global effect in the vestibular periphery.

Adenosine is not responsible for local metabolic control of coronary blood flow in dogs during exercise.

The purpose of this investigation was to quantitatively evaluate the role of adenosine in coronary exercise hyperemia. Dogs (n = 10) were chronically instrumented with catheters in the aorta and coronary sinus, and a flow probe on the circumflex coronary artery. Cardiac interstitial adenosine concentration was estimated from arterial and coronary venous plasma concentrations using a previously tested mathematical model. Coronary blood flow, myocardial oxygen consumption, heart rate, and aortic pressure were measured at rest and during graded treadmill exercise with and without adenosine receptor blockade with either 8-phenyltheophylline (8-PT) or 8-p-sulfophenyltheophylline (8-PST). In control vehicle dogs, exercise increased myocardial oxygen consumption 4.2-fold, coronary blood flow 3.8-fold, and heart rate 2.5-fold, whereas mean aortic pressure was unchanged. Coronary venous plasma adenosine concentration was little changed with exercise, and the estimated interstitial adenosine concentration remained well below the threshold for coronary vasodilation. Adenosine receptor blockade did not significantly alter myocardial oxygen consumption or coronary blood flow at rest or during exercise. Coronary venous and estimated interstitial adenosine concentration did not increase to overcome the receptor blockade with either 8-PT or 8-PST as would be predicted if adenosine were part of a high-gain, negative-feedback, local metabolic control mechanism. These results demonstrate that adenosine is not responsible for local metabolic control of coronary blood flow in dogs during exercise.